"I'll admit it here - I have shaved a grown man before," laughs Johnny Depp, who lathers his customers before gruesomely slitting their throats as the eponymous murderer in new musical Sweeney Todd: The Demon Barber Of Fleet Street, out Friday January 25. "He is alive," says Johnny of his 'client'. "He's walking round to this day."

The movie - for which he has just scooped a Best Actor Golden Globe - provided a new challenge for the 44-year-old star, whose chameleon-like ability to slip into any character and make him interesting and original is legendary. But Sweeney Todd wasn't about mere acting.

"I had never sung a song," reveals Johnny, who used to play guitar in an Eighties band called The Kids, as well as providing back-up axe on an Oasis track. "I was the guy who would come in and sing the harmony, very quickly. It would be all of three seconds and then I was out."

However, he admits that music was always his first love. "I wanted to be a rock star," he says. "I didn't even think about acting. I was a musician for years and years before I did a movie."

So when long-time collaborator Tim Burton came asking him to take on Sweeney - based on the famously-intricate Stephen Sondheim stage musical - Johnny decided to participate in his own mini-X Factor. He called ex-bandmate chum Bruce Witkin and went into the studio to record one of the film's songs, on the proviso that Witkin told him truthfully if he had the vocal ability to pull off the entire movie.

"I said 'Do you want the good news or the bad news?'" remembers Witkin. "He said, 'Well, give me the bad news'. And I said, 'The bad news is you're going to have to do this'."

Johnny signed up, playing the doomed anti-hero who turns to murder after his family is stolen from him and he is unjustly imprisoned for 15 years. He is joined by Helena Bonham Carter as his accomplice Mrs Lovett, the lady who comes up with the plan to dispose of the dead bodies by turning them into delicious pies. The rest of the cast includes Alan Rickman as baddie Judge Turpin and Timothy Spall as the evil Beadle Bamford.

"[Sweeney's] obviously a dark figure," explains Johnny. "But I think hyper-sensitive. He has experienced something very dark and traumatic in his life, a grave injustice and I always saw him as a victim. Anyone who is victimised to that degree and then turns around and becomes a murderer can't be all there."

Complete with gothic wardrobe and bouffant locks highlighted by a shocking streak of white, the actor ends up sounding pretty good, even drawing comparisons to the man formerly known as Ziggy Stardust.

"A couple of people have said that," he grins. "I wouldn't dream of attempting to channel David Bowie, because he's a big hero of mine. If there's a similarity, it wasn't intentional." In fact, after interpreting Keith Richards to play Captain Jack Sparrow in the Pirates Of The Caribbean trilogy, Johnny says Sweeney and his Cockney brogue is not based on anyone in particular. The voice, he says, comes "just from spending time over [in Britain]".

The UK is now only a short hop from his base in France, where he lives with his two children and girlfriend Vanessa Paradis. "I don't hang out with anybody who is famous," he says of his laid-back Gallic existence. "I don't know who is rich or poor or successful and it feels good."

Indeed, he manages to pretty much stay out of the tabloids altogether, relishing his family time. "I just want to spend as much time with my kids as possible," he says. "Doing simple things like going out to the trampoline and swing set, or just looking in the garden to see how the tomatoes are doing - old man stuff."

The time he spent away from home was brought into sharp focus last year, when eight-year-old daughter Lilly Rose was rushed to hospital suffering from Ecoli food poisoning.

Luckily, she is fully recovered, but as he told American mag Entertainment Weekly: "To say it was the darkest moment, that's nothing. Now, every single milli-second is a mini-celebration."

Basking in his Golden Globe success, Johnny is currently preparing for several upcoming projects, including director Michael Mann's period gangster pic Public Enemies, opposite Christian Bale and the long-gestating Shantaram, in which he is due to play an ex-heroin addict-turned doctor to the poor in India.

One thing he is unlikely to tackle again, despite the plaudits, is another musical. Blame the fact that although once he got over the initial fear "it was kind of enjoyable", he was unprepared for the on-set embarrassment. "We thought we were going to lip-sync," he recalls of pre-production. "You go in the studio and sing your guts out and do it the best you can. But the only way to do it is to belt it out again on the set, which was extremely mortifying because everyone's very, very close and you feel like an idiot! So, would I do it again? I doubt it."

Real Name: John Christopher Depp II

Age: 44

Significant Other: French singer and actress Vanessa Paradis

Career High: Oscar nominations for Finding Neverland and Pirates Of The Caribbean and A Golden Globe for Sweeney Todd

Career Low: The late 1990s were a blur of booze, drugs and brawls

Famous For: Trying hard to shun boring leading man roles in favour of odd characters

Words Of Wisdom: "I cannot take this job seriously. There's nothing worse than those actors who give the impression they've taken on the priesthood. At the end of the day, acting is really about lying, and in my case, drinking coffee."